VARIATIONS OF MILK CONSTITUENTS 



1 6s 



point we shall call attention only to the general 

 relation in different milks and *to the conditions 

 which influence this relation, leaving the various 

 application of the facts to later chapters. We have 

 already noticed the percentages of fat and of casein 

 in milk and some of the conditions which cause 

 variation. We now come to consider whether fat 

 and casein vary alike ; that is, whether fat and casein 

 have the same relation to each other in milk under 

 all conditions. We will consider this phase of the 

 subject under the following divisions: (i) Individ- 

 uality, (2) breed, (3) stage of lactation, and (4) fresh 

 pastures and drouth. 



Influence of individuality upon relation of fat 

 and casein. — The results of the work done at the 

 New York experiment station and elsewhere have 

 shown that the relation of fat and casein varies greatly 

 in the milk of different individuals, the variation being 

 greatest, of course, in the case of single milk- 

 ings. This fact has been well recognized for 15 

 years or more and is too familiar even to need illus- 

 tration. 



Influence of breed upon relation of fat and 

 casein. — The following data are taken from those 

 already given on preceding pages. 



Name of breed 



Holstein-Friesian. . . . 



Ayrshire 



American Holdemess 



Shorthorn 



Devon 



Guernsey 



Jersey 



Per cent 

 of fat 



3.26 

 3.76 

 4.01 

 4.28 

 4.89 

 5.38 

 5.78 



Per cent 

 of casein 



2.20 

 2.46 

 2.63 

 2.79 

 3.10 

 2.91 

 3.03 



Parts of casein for 

 one part of fat 



Fat; Casein 



0.67 

 0.6S 

 0.66 

 0.65 

 0.63 

 0.54 

 0.52 



